Short answer: Signing a PDF means adding your signature to a PDF page by drawing it, uploading a ready-made signature image, or typing your name, or creating a cryptographic signature with a digital certificate. Visual signatures are fast and practical; for official transactions and situations where a secure electronic signature is expected between parties, a certificate-based cryptographic signature is preferred.
What is signing a PDF and which methods are used?
Signing a PDF is the process of showing that a document is approved by adding a signature image or cryptographic signature data to it. This lets a document be approved digitally without printing it out and signing it by hand.
In practice, four common methods are used:
- **Drawing:** You draw your signature by hand with a mouse, trackpad, or touchscreen. It gives the visual result closest to a wet signature.
- **Uploading an image:** You add a signature you previously scanned or photographed as an image file to the PDF.
- **Creating from text:** You type your name and convert it into a handwriting style to produce a signature image. This is a practical solution if your handwriting does not look good on screen.
- **Cryptographic signature:** You add a mathematically verifiable signature to the PDF with your personal digital certificate; if the document is changed, the signature becomes invalid.
Visual signature methods amount to a declaration that "I approve this document." A cryptographic signature, on the other hand, makes the signer's identity and the document's integrity technically verifiable.
How do you sign a PDF online? Step by step
The basic flow for signing a PDF online is to prepare the signature image, place it on the document, and save it. Although the method you choose may differ, the steps are largely the same:
- Prepare the document: Open the PDF you want to sign and find the page where the signature will go.
- Decide on your signature source: You will either draw the signature on screen, upload a ready-made image, or type your name and choose a handwriting style. If you need a text-based signature image, you can use the [Personal Signature Generator](/tool/signature-generator).
- Create the signature: Produce the signature image with the method you chose. If you are uploading an image, choosing a high-resolution file with a clean background makes the result sharper.
- Place it on the document: Move the signature to the correct position on the page and adjust its size to match the signature area in the document. If there is no signature field, check the margins and line alignment.
- Save and download: Complete the process and download the signed PDF. You can use the [Sign PDF](/tool/sign-pdf) tool to add a signature to a PDF.
- Send it to the other party: Forward the signed file by email or a sharing link.
If multiple pages need to be signed, a separate signature must be added to each signature area; placing the signature in the relevant fields rather than applying a single signature image "in bulk" across the whole document gives a more accurate result.
What is the difference between a visual signature and a cryptographic signature?
A visual signature is an image added to the document; a cryptographic signature is verifiable data tied to the document's contents. Although these two methods may look like alternatives to each other, their purposes differ.
| Criterion | Visual signature (drawing/image/text) | Cryptographic signature |
|---|---|---|
| What does it add? | A signature image | Signature data tied to a certificate |
| Verification | Visual check | Technical check with signature verification tools |
| Document modification | May go unnoticed afterwards | The signature becomes invalid |
| Proof of identity | Based on the signature image | Based on the certificate holder |
| Typical use | Internal correspondence, forms, quotes, contract drafts | Official applications, corporate approvals, legal processes |
In Turkey, a secure electronic signature under Electronic Signature Law No. 5070 produces the same legal result as a handwritten signature. Therefore, if the document carries high legal weight, a certificate-based signature is required instead of a visual signature. For this kind of signature, you can use the PDF Cryptographic Signature tool with your own certificate file.
Which signature method should you choose in which situation?
Which method is appropriate depends on where and by whom the document will be accepted. You can use the following distinction when making your choice:
- **Internal company forms, leave requests, quotes:** A visual signature is usually enough; the process moves quickly.
- **Contracts with customers:** It depends on the parties' agreement and the contract text. If the parties accept electronic signatures, a visual signature can be used; otherwise a secure electronic signature is requested.
- **Applications to official institutions:** A secure electronic signature made with a qualified electronic certificate is generally expected.
- **Documents that only need a read/approved note:** A simple signature created by typing your name and adding the date may be enough.
If it is critical to know whether the document was changed afterwards, a cryptographic signature should be chosen, because with this method the smallest change to the document invalidates the signature.
How do you proceed with PDFs that more than one person must sign?
If there are multiple signers, the signing process needs to be tied to a sequential or parallel flow. In a sequential flow, each signer waits for the previous one to finish; in a parallel flow, invitations are sent to all signers at the same time.
Points to keep in mind in such a process:
- Clarify the signer list: Determine from the start who will sign, in what order, and on which page.
- Choose the flow type: Use a sequential flow if the order of approval matters, or a parallel flow if time is limited.
- Send the invitations: Clearly tell each signer the link to the document and what they need to do.
- Keep the audit trail: Archive the record showing who signed and when. This record is useful in disputes that may arise later.
- Lock the final version: Once all signatures are complete, inform the parties that the file must not be changed.
To prepare a PDF with multiple signers, you can use the PDF Multi-Signer Workflow tool.
How do you check the validity of a signed PDF?
The validity of a signed PDF is checked with different methods depending on the type of signature. With a visual signature, the check is done visually; with a cryptographic signature, the signature data must be verified technically.
The following information is examined when checking a cryptographic signature:
- **Signature validity:** Does the signature data match the document, and has the document been changed since it was signed?
- **Signer:** Which certificate holder applied the signature?
- **Signature date:** On what date and at what time was the signature created?
- **Certificate provider:** Which certificate authority issued the signature?
To perform this check, you can use the e-Signature Verification (PDF) tool.
Before sending a signed PDF to another signer, it is important to forward the file in an uncompressed and unconverted form. Converting the PDF to another format and then back to PDF can invalidate the cryptographic signature.
Frequently asked questions
Is a visual signature on a PDF legally valid?
The validity of a visual signature depends on the context in which the document is used and the agreement between the parties. If the parties accept electronic approval, a visual signature works; for official transactions, a secure electronic signature under Law No. 5070 is required.
Can I draw my signature on my phone and add it to a PDF?
Yes. You can draw your signature with your finger or a stylus on the touchscreen, save it as an image, and add it to the PDF. Alternatively, you can type your name and convert it into a handwriting style to produce a signature image.
What happens if a signed PDF is changed afterwards?
In a PDF with a visual signature, a change may not be noticed immediately. In a PDF with a cryptographic signature, any change made to the document invalidates the signature, and this is seen during verification.
Can more than one signature be added to the same PDF?
Yes. For documents that more than one person must sign, a sequential or parallel signing flow can be set up. Determining from the start which page and in what order each signer will sign prevents confusion.
What do I need for a cryptographic signature?
A cryptographic signature requires a digital certificate file that belongs to you. A PDF signed with a certificate can be checked in signature verification tools along with the signer, date, and certificate provider information.